74 AGE OF TREES AND WOODS. 



tree (Hornbeam, Alder). In the case of suppressed trees the 

 true rings are frequently so narrow, either all round or in parts, 

 that they are difficult to distinguish. 



The business may be facilitated by smoothing the surface, 

 by making a slanting cut, or by applying] colouring matters (as 

 indigo, alizarine ink, Prussian blue, alcohol coloured with 

 aniline, sulphuric acid, etc.). Such colouring does, however, 

 not always facilitate the counting. 



The number of rings thus counted represents only the age 

 of the tree above the place where it has been cut. To the 

 number so obtained the number of years which the tree took 

 to reach that height must be added. If it is desirable to 

 avoid mistakes in this respect, the stool must be split open 

 along the centre and the rings counted to the starting point. 



In this way the physical age of the tree can be ascertained, 

 provided that each concentric ring represents a year's growth. 

 It is, however, by no means certain whether this is always the 

 case, as temporary interruptions of growth may cause two rings 

 to be formed in one year. (For instance, the destruction of 

 the leaves by insects and the subsequent sending forth of a 

 second crop of leaves, fire running through a wood, or even 

 late frost.) Moreover, there are trees in the tropics on which 

 the concentric rings do not exist, or cannot be distinguished. 



Another point is, that a distinction must be made between 

 the physical and economic age of a tree. By the latter is 

 understood the actual growing age, leaving out of consideration 

 any years during which the tree may have been at a stand-still, 

 owing for instance to heavy shade from above. 



2. Determination of the Age of Whole Woods. 



a. Even-aged Woods. 



If the age of such woods is not known from authentic 

 records, it can be ascertained by determining the age of a 

 tree by one of the methods indicated above. If a tree is felled 

 for the purpose of counting the concentric rings, it is desirable 



